arp with
no mode specifier will print the current content of the
table. It is possible to limit the number of entries
printed, by specifying an hardware address type, interface
name or host address.

arp -daddress will delete a ARP table entry. Root or
netadmin privilege is required to do this. The entry is
found by IP address. If a hostname is given, it will be
resolved before looking up the entry in the ARP table.

arp -saddress hw_addr is used to set up a new table entry.
The format of the hw_addr parameter is dependent on
the hardware class, but for most classes one can assume that
the usual presentation can be used. For the Ethernet class,
this is 6 bytes in hexadecimal, separated by colons. When
adding proxy arp entries (that is those with the
publish flag set) a netmask may be specified
to proxy arp for entire subnets. This is not good practice,
but is supported by older kernels because it can be useful.
If the temp flag is not supplied entries will be
permanent stored into the ARP cache. To simplify setting up
entries for one of your own network interfaces, you can use
the arp −Dsaddress ifname form. In that
case the hardware address is taken from the interface with
the specified name.

When setting or reading the ARP
cache, this optional parameter tells arp which class
of entries it should check for. The default value of this
parameter is ether (i.e. hardware code 0x01 for IEEE
802.3 10Mbps Ethernet). Other values might include network
technologies such as ARCnet (arcnet) , PROnet
(pronet) , AX.25 (ax25) and NET/ROM
(netrom).

−a

Use alternate BSD style output format (with no fixed
columns).

−e

Use default Linux style output format (with fixed
columns).

−D,
−−use-device

Instead of a hw_addr, the given
argument is the name of an interface. arp will use
the MAC address of that interface for the table entry. This
is usually the best option to set up a proxy ARP entry to
yourself.

−iIf,
−−deviceIf

Select an interface. When
dumping the ARP cache only entries matching the specified
interface will be printed. When setting a permanent or
temp ARP entry this interface will be associated with
the entry; if this option is not used, the kernel will guess
based on the routing table. For pub entries the
specified interface is the interface on which ARP requests
will be answered.
NOTE: This has to be different from the interface to
which the IP datagrams will be routed. NOTE: As of
kernel 2.2.0 it is no longer possible to set an ARP entry
for an entire subnet. Linux instead does automagic proxy arp
when a route exists and it is forwarding. See arp(7)
for details. Also the dontpub option which is
available for delete and set operations cannot be used with
2.4 and newer kernels.

−ffilename, −−filefilename

Similar to the −s
option, only this time the address info is taken from file
filename. This can be used if ARP entries for a lot
of hosts have to be set up. The name of the data file is
very often /etc/ethers, but this is not official. If
no filename is specified /etc/ethers is used as
default.

The format of
the file is simple; it only contains ASCII text lines with a
hostname, and a hardware address separated by whitespace.
Additionally the pub, temp and netmask
flags can be used.

In all places
where a hostname is expected, one can also enter an
IP address in dotted-decimal notation.

As a special
case for compatibility the order of the hostname and the
hardware address can be exchanged.

Each complete
entry in the ARP cache will be marked with the C
flag. Permanent entries are marked with M and
published entries have the P flag.